Commercial wireless BAS

The protocol, applications, and design approach for wireless sensor expansion in commercial BAS are in a state of flux, and are moving forward quickly.

John Huston, PE, exp Global Inc., Chicago

10/24/2011

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Wireless technologies offer attractive opportunities to reduce capital construction costs for commercial BAS through reduction in installation labor. Installation of wireless sensing devices eliminates the labor required to open walls, abate asbestos, run wiring and conduit, and work after hours. Typically, installation labor represents 50% to 60% of the cost to install a BAS. Wireless technology can reduce the labor required to install a single space temperature sensor by 90% to 95%. For example, the labor required to install a space temperature sensor for a variable air volume (VAV) terminal unit is reduced from 2 hours (hardwired through the wall) to only 10 minutes.

The functionality and innovation of wireless devices enable a high degree of design flexibility in a variety of applications. The list of applications and success stories grows every day; for an overview of how wireless technology is being applied, see the ZigBee Alliance and EnOcean Alliance examples.

While reduction in installation cost and increased functionality are attractive features, do wireless sensing systems meet the open protocol expectations that have evolved in the BAS market (such as LonMark, BACnet, DALI, and Modbus)? Can wireless systems be designed to be cost effective over the lifecycle of the facility? Are today’s wireless technologies, products, and business models up to the open business challenge? The potential is there, but these questions must be addressed before wireless technologies are used in a BAS design.

Signals and codes

We are barraged with wireless communication signals every day. Wireless signals effectively deliver data for a wide variety of applications including telecommunications, TV, radio, satellite, and computer networks. These signals are transmitted over various media including radio frequency (RF) and infrared (IR). These technologies are proven for other markets, but can wireless technology be cost-effectively applied to the commercial building automation system market?

Of the wireless technologies currently available, RF technology is the most promising, as it has the highest level of interest, participation, development, and implementation with regard to the commercial building automation market.

Leading the way are industry organizations that have formed to develop and promote wireless technologies, standards, and applications for the residential and commercial building markets. The members of these organizations, including manufacturers, integrators, and end users, are actively developing the means and methods for effectively applying wireless solutions. The mass market driver and business model for most wireless devices is currently more attractive to the high-volume residential market.

The challenge is that the technologies being developed for the commercial building automation market must be significantly more robust than the technologies that historically have been applied in the residential market. Commercial wireless systems must overcome barriers such as application development, integration, support, interoperability, security requirements, interference from noise and obstructions, and codes and FCC regulations. The technologies and standards have to be flexible enough to allow innovation while restrictive enough to promote interoperability and interchangeability. Fortunately, wireless industry organizations are developing standards and technologies to satisfy both the low-cost, high-volume residential and more robust commercial markets. This dual application will create profitable business models and continual advancement of the wireless market in the long term.

Where is the market today?

As wireless technologies and standards (such as IEEE 802.15.4) advance, a multitude of products are hitting the market. The manufacturers providing these products vary from start-ups to major corporations, each with its own viewpoint on how a wireless device should perform. Before designing wireless devices into a control system, the products and systems must be thoroughly evaluated to determine how they will perform in the desired applications. Several key factors must be considered:

Application

Functionality

Products

Radio frequency (Hz)

Signal strength and distance

Security

Network architecture

Protocol

Interoperability

Interchangeability

Lifecycle cost

Support.

Wireless devices for commercial BAS vary in their approach to all of these factors. As a result, the wireless commercial BAS market is proprietary. The devices and systems offer initial design and implementation flexibility but have significant lifecycle limitations. Since the systems are not interchangeable, the operation, maintenance, upgrade, and expansion of a wireless commercial BAS sensing system is typically limited to a sole source provider after the initial installation.

To maximize the performance of wireless devices throughout the lifecycle of the facilities, the client’s objectives must be thoroughly understood, the applicable products must be researched, and the system must be designed, specified, and implemented to meet the requirements, goals, and expectations. Developing a wireless project with only performance specifications and vague requirements will most likely result in disappointment.

Detailed design and thorough specification are necessary to define the desired performance of a wireless system, whether it be stand-alone or part of a bigger system. Wireless technology is in its infancy relative to the commercial controls market. Standards, products, and applications are all under active development. Therefore, extra attention must be paid to understand how these continually evolving products can be effectively integrated into a commercial BAS. It is possible, but it takes some effort to research, understand, and effectively apply the options.

The impact of each of the key factors listed above must be understood before design and specification can begin.

Application: The desired application must be considered from both functionality and product perspectives.

Functionality: What purpose will the wireless device perform? The intent of the operation of the device must be clearly defined to determine if wireless technology will provide value. How will performance be quantified and measured? What other systems do the wireless devices need to share information with, and what kind of information will be shared? Taking the time to thoroughly define the intent will pay dividends during the design.

Products: Are products available to address the functionality? Continuing education is especially important for emerging technologies to maximize performance. Keeping track of the functionality of a growing list of wireless products is a daunting but necessary task. Stay engaged with the technology by participating in industry organizations, webinars, and trade shows.

Radio frequency (Hz): IEEE 802.15.4 identifies 2.4 GHz as a global frequency with regional frequencies of 915 MHz (Americas) and 868 MHz (Europe). The operations in some commercial facilities are sensitive to certain frequencies, and therefore the facility’s IT group may restrict the devices that can be utilized. A popular standard utilizes a 2.4 GHz signal, and manufacturers offer a number of products that are built on that frequency. While 2.4 GHz is a frequency that should enable use worldwide, it is important to discuss frequency restrictions with the corporate IT group that owns the facility to identify the range of acceptable frequencies. Do not assume that a frequency can be used in a facility just because it is licensed nationally.

In a recent design, 2.4 GHz devices were prohibited from a data center application because of potential interference with sensitive equipment. The design was converted to use 868 MHz devices and as a result changed the list of approved manufacturers. This frequency restriction was identified by the IT group in the data center during the investigation phase and was addressed before the design was produced. Signal strength and distance:

Signal strength and distance are closely related. The stronger the signal, the farther it will travel. However, the stronger the signal, the more power it consumes and the more likely it is to interfere with other devices and systems. There is always a trade-off to consider. Wireless devices are typically designed for indoor applications over small distances; therefore, the distance a signal will travel is limited. The effective distance will be further reduced by obstructions. The manufacturers provide design guidelines and estimated distances between devices and/or repeaters to provide the basis for system layout. The distance estimates are critical to the design because they will determine the location and quantity of the devices.

It is important to remember that the quality and reliability of RF communication can be significantly impacted by the surrounding environment, as can any signal that is transmitted in an open media and exposed to unknown sources of interference. The distance specified in the design guide may not be achievable once installed on-site due to the effect of unknown conditions. Most manufacturers provide test transmitters and receivers to test signal strength and quality throughout a facility. Since wireless devices for commercial BAS are primarily installed in existing facilities, the signal strength can be physically tested. A signal test prior to system design will provide valuable data to optimize the design. Repeaters can be added to boost signal strength if required.

Testing also applies to the construction phase. Testing the signal strength before device installation should be a specification requirement, witnessed by the design engineer, to verify the submitted solution will work properly. If the signal is weak, repeaters can be added as required to boost the signal.

Security: Security is a primary concern for mission critical and sensitive facilities. Do not assume a client will allow the use of wireless devices. Many secure and unsecure facilities do not allow wireless devices for many reasons, including the perception that the communication messages can be intercepted or interfered with from outside the facility. To ease this concern, encryption may be provided to meet heightened security requirements. Not all wireless device manufacturers enable encryption, so if security is an issue the list of available devices may be considerably restricted.

Network architecture: Wireless network architectures have two primary structures: mesh and hub. Mesh networks are more popular. They are “flat,” meaning they do not have a device hierarchy. All devices in the network are peers. In a mesh network every device is both a receiver and a transmitter. Each device acts as a repeater, relaying messages from one device to another. Mesh networks automatically and dynamically configure themselves to “speak” with neighboring devices that have the strongest signal. This creates a self-healing network. If a device drops out and stops communicating, the remaining devices will search for other device signals and automatically reroute traffic.

Hub networks (Figure 1) use a centralized intelligent “hub” device to communicate to a number of individual lower-level “spoke” devices. The hubs then communicate to each other over wired or wireless media. The hub architecture has a potential cost advantage through the use of higher quantity, lower cost “dumb” spoke devices while using lower quantity, higher cost “intelligent” hubs to manage communication, store data, and provide a user interface. The hub architecture has the disadvantage of being susceptible to single points of failure. If a hub goes down, communication to all spokes is lost.

Protocol: The protocol used by each device and the rules for message communication are important to understand. The protocols define the languages that the devices “speak.” Devices that speak different languages cannot communicate with each other without translation. All devices in a wireless system must use the same protocol and transmission rules; otherwise, gateways must be provided to provide protocol translation.

Interoperability: Interoperability is defined as the capability of one system or device to speak with a system or device from another manufacturer, be it wired or wireless. There are a few mainstream open protocols for the BAS market that promote interoperability including BACnet, LonWorks, and Modbus. Most wireless networks do not speak BACnet, LonWorks, or Modbus as the wireless protocol but offer gateways to convert the wireless protocol to BACnet, LonWorks, and/or Modbus. Gateways should only be used when absolutely necessary, as they complicate the design, maintenance, and support of the systems, and create single points of failure.

Interchangeability: Interchangeability is the ability to integrate devices from two or more manufacturers into the same network, including the flexibility to replace a device from one manufacturer with a functionally identical device from another manufacturer. Interchangeability is what most end users define as an open system. Interchangeability promotes open, competitive business throughout the lifecycle of the facility.

Lifecycle cost: The lifecycle cost for wireless sensing systems with commercial BAS is comprised of many facets including initial installation, maintenance, upgrade, and expansion. Wireless sensing systems for commercial BAS are single vendor solutions. These systems are restrictive with regard to services that are provided after the initial installation, including maintenance, upgrade, and expansion. The design must consider the lifecycle cost if the primary intent is to reduce cost. Savings achieved during the initial installation may be lost a few years down the road through expensive service contracts or, worse yet, when manufacturers go out of business and products become unavailable. The strength and longevity of the manufacturer/vendor should be a key evaluation factor when selecting a solution. The specifications should require the use of current production, off-the-shelf products that have been installed in three to five similar applications with a 2- to 4-year production history. Do not risk system reliability and sustainability by allowing the use of obsolete or first-run products.

Support: Support is critical to maximize long-term operation. Quality products, manufacturers, designers, and integrators are necessary to support the system from concept development and design through implementation and operation. All aspects of the delivery chain must be validated or long-term performance will be jeopardized. Once the design is developed, the specification should identify acceptable manufacturers. The specification should also stipulate that the contractor be an authorized distributor of the manufacturer and a certified system integrator.

Wireless industry organizations

The wireless industry organizations that are leading the way to developing wireless technology for commercial BAS applications are ZigBee, Z-Wave, and EnOcean. These three organizations comprise a wide variety of innovative and well-known member companies, promoters, participants, and adopters. A quick look at these websites provides a good overview of the progress that has been made and the products that are available. The companies listed on these websites provide a good place to start a wireless application investigation, but they do not represent all providers of equipment that use these wireless standards.

Investigation of the current products available on the market reveals a heavy slant toward the residential market. The products available for the commercial market are slim. Why is that? What does that mean for the future? As stated earlier, my opinion is that technology is more than capable of supporting the commercial market. It is being created to properly address the challenges of commercial environments, but the emerging wireless market must be nurtured. The issue is that commercial wireless technology and products are relatively new, and the commercial BAS market does not adopt new technologies overnight. Therefore, a variety of manufacturers are developing devices for the residential market because it is quicker to respond, has lower capital investment for the user, has a certain percentage of early adopters or “techies” that like to experiment with the latest and greatest new products, and represents a large potential mass market. It’s only a matter of time before more of these products migrate into commercial BAS applications.

Mission critical data center

The standard of 99.99% uptime is a target for mission critical data centers. To achieve this goal, a data center can only have downtime of 52 minutes a year. Integrating advanced control systems and analytics to help achieve high reliability represents an opportunity for wireless networks to provide high value at low cost. Precise temperature control is necessary to maintain the operation of the servers on the data center floor.

Typically data centers are designed with redundancy of 2N or 2N + 1, requiring the installation of duplicate computer room air conditioners (CRACs) and other equipment to guarantee environmental control. The CRACs typically control based on return air temperature that is sensed inside the unit. The CRACs will maintain setpoints and send alarms to a network operation center if return air temperature drifts outside a preset range. Alarming based on CRAC return air is not the best method to maintain the health of the individual servers. For example, if there is a problem with the airflow through the data center because a floor tile was left open, or due to a malfunctioning server, hot spots may be created in isolated areas. These isolated hot spots are not detected because they blend in with the return air and may eventually lead to premature failure of the server.

The solution is to measure spot temperatures throughout the data center floor using an 860 MHz mesh network of wireless temperature sensors with 3-ft flexible probes, hung from the ceiling at specific locations (see Figure 2). These temperature sensors provide point monitoring of hot and cold aisles to insure that proper cooling and airflow are maintained throughout the data center. The wireless sensors are connected to the network controller for the data center through a communication gateway that converts the wireless protocol to LonWorks. The enterprise-based graphical user interface controls and monitors all of the HVAC, lighting, power, security, and fire suppression systems for the entire data center. The wireless sensing network was added as a relatively low-cost and powerful enhancement to improve the overall reliability.

A wired solution would not have been flexible enough to address the dynamic environment that must be maintained on the data center floor. Servers are continually added and/or removed. The wireless network enables the sensors to be relocated, and alarm parameters to be adjusted as required to address the dynamic nature of the data center percent capacity and layout.

Point-to-point wireless sensing

A major cost factor for terminal units is the labor to install the space temperature sensor. The space temperature sensor can be mounted a considerable distance from the terminal unit controller (e.g., VAV box), requiring large amounts of conduit and wiring throughout the facility. At least one open protocol control system manufacturer has utilized wireless and battery-less space temperature sensors to communicate point to point, from a wireless space temperature transmitter to a wireless receiver in the VAV box controller. The time and materials to install a space temperature sensor are reduced to just a few minutes with no virtually no expense for conduit and wiring, or cutting and patching. The battery-less feature uses a small photovoltaic to power the sensor off ambient light and a capacitor to store the energy when the lights are off. The VAV box controller also has the option to hardwire a temperature sensor if for some reason the wireless signal is blocked.

Can wireless devices work in commercial BAS?

The short answer is yes. Zigbee, Z-Wave, and EnOcean wireless sensing systems are being integrated into commercial BAS worldwide by a variety of providers, in a variety of applications.

The long answer is yes, but lifecycle costs and sustainability play an important role in the decision to go wireless. The designer must understand the benefits and restrictions of wireless technology in order to develop solid business opportunities for commercial facilities.

Wireless devices can be effectively applied in a variety of building automation applications. Designers and users will be happy with the performance provided that they research not only the features and benefits but also the constraints and limitations.

Proper design requires due diligence on the application side as much as on the product side. The client’s goals and expectations are integral to the design and may justify the constraints and limitations.

Although the approach to wireless system design is currently “up in the air,” many talented individuals are working overtime to develop products, solutions, and applications that will bring the opportunities down to earth.

Huston is vice president of technology integration with exp Global. His experience includes more than 25 years designing and implementing advanced control systems for a wide variety of public and private clients.